1. Field
The following description relates to a touch screen panel.
2. Description of the Related Art
A touch screen panel is an input device capable of selecting a content indicator displayed on a screen of an image display device using a human hand or an object to input the command of a user.
The touch screen panel is provided on a front face of the image display device to convert a contact position of the human hand or the object into an electrical signal. Therefore, the content indicator selected at the contact position is received as an input signal.
Because the touch screen panel may replace an additional input device coupled to the image display device, such as a keyboard and/or a mouse, the range of use of touch screen panels is gradually increasing.
Methods of operating a touch screen panel include a resistance layer method, a photo-sensing method, and an electro-capacitive method. Among the above methods, the widely used electro-capacitive touch screen panel senses a change in capacitance in an area formed by conductive sensing cells along with other peripheral sensing cells when the human hand or the object, such as a stylus pen, contacts the touch screen panel to convert the contact position into the electrical signal.
For this purpose, the electro-capacitive touch screen panel includes first sensing cells formed along a first direction, second sensing cells formed along a second direction, first coupling patterns for coupling the adjacent first sensing cells along the first direction, and second coupling patterns for coupling the adjacent second sensing cells along the second direction.
The touch screen panel is commonly attached to an external surface of an image display device, such as a liquid crystal display (LCD) or an organic light emitting display. Therefore, high transparency and thin-film characteristics are required. In particular, the touch screen panel is designed so that the sensing cells and the coupling patterns are not visible to a user.
Recently, a flexible image display device has begun development. Therefore, the touch screen panel attached onto the flexible image display device must be flexible as well.
In a conventional touch screen panel, sensing cells are formed of a transparent, conductive material, such as indium tin oxide (ITO). However, in this case, when the conventional touch screen panel is curved or folded, cracks will be generated in the sensing cells such that the operation of the touch screen panel may be negatively affected.
In addition, in the conventional touch screen panel, because a thin-film forming process and a pattern forming process are required to form the sensing cells, high heat resistance and chemical resistance are also required. Therefore, the sensing cells are usually formed on a glass substrate suitable for these processes.
However, in this case, because the glass substrate must have a thickness no less than a uniform value such that the glass substrate may be produced, the glass substrate cannot be formed to have a sufficiently small thickness or be flexible.
In order to apply the conventional touch screen panel to the flexible image display device, use of a flexible thin film such as polyethylene terephthalate (PET) as the substrate of the touch screen panel has been suggested. However, controlling the area and/or width of the sensing cells and coupling patterns formed on the thin film is difficult. In particular, because the coupling patterns are formed to have a width less than a width of the sensing cells, electrical transmittance and a low surface resistance condition (e.g., a predetermined surface resistance condition) must be ensured.
When the conventional touch screen panel is manufactured using the glass substrate, the first or second coupling patterns are formed of an opaque metal in the form of a wire. However, when the flexible touch screen panel is manufactured using the thin film, it is difficult to perform the high temperature process due to the flexible thin-film material having lower heat resistance, such that the high temperature process is limited, thereby causing the width of the coupling patterns to be increased.
Therefore, in the flexible touch screen panel, the coupling patterns are visible, and preventing the coupling patterns of the flexible touch screen panel from being visible is desired.